This invention concerns hexacoordinated compounds of Mn, Fe, Co and Ni, and fuel compositions containing them.
The octane quality of a fuel is an important indication of the power, efficiency and economy the fuel will deliver to internal combustion engines which run on it. One way to increase the octane quality of a fuel is to increase the amount therein of high octane hydrocarbon components such as benzene, toluene and the like. An alternate way to increase octane quality is to incorporate antiknock additives into the fuels.
In the past, tetraalkyllead compounds were regularly used by refiners as an additive to increase octane quality. With the advent of automobiles equipped with catalytic converters for exhaust emission control purposes has come the attendant requirement for lead-free gasolines. The alternative of increasing the high octane hydrocarbon components of the fuel is not particularly acceptable for improving octane quality, such components being more valuable when used as solvents or petrochemical feedstocks.
Nonlead antiknock additives, both metal-containing and metal-free, have been suggested as replacements for tetraalkyllead antiknocks. These additives have not attained widespread use because of one or more deficiencies in their antiknock activity, hydrolytic or oxidative stabilities or fuel solubility. Accordingly, there is a need for effective and stable nonlead additives to improve fuel octane ratings.
Certain metal (nonlead) beta-diketone compounds have been suggested as antiknock additives for hydrocarbon fuels. Said beta-diketone compounds have low fuel solubility and low volatility, however, and have not been used commercially. See British Pat. No. 287,192 and U.S. Pat. Nos. 2,114,654 and 2,156,918.
Studies such as the following: Graddon, Nature 195, 891 (1961), "Polymerization of Transition Metal Beta-Diketone Chelates,"; Cotton and Elder, J. Am. Chem. Soc., 86, 2294 (1964) "The Tetrameric Structure of Anhydrous Crystalline Cobalt (II) Acetylacetonate"; and Graddon, Cord. Chem. Rev., 4, 1 (1969), indicate that the tetracoordinated acetylacetonates of Mn, Fe, Co, and Ni are polymerized (trimers and tetramers) in the solid state and in nonpolar solvents. The oligomeric nature of these compounds most probably explains their low solubility in gasolines and their low volatility.
It is known to prepare divalent transition metal chelates of beta-diketones which are monomeric in the solid state and in nonpolar solvents by using a beta-diketone with bulky groups such that the steric contributions of the bulky groups in the chelate compounds preclude self-polymerization of the chelate compounds. Thus, chelate compounds of divalent transition metals with 2,2,6,6-tetramethyl-3,5-heptanedione (dipivaloylmethane, DPM) are reported to be monomeric in the solid state and in nonpolar solvents. However, while the presence of bulky groups in beta-diketone provide monomeric chelate compounds, such compounds are not practical for most uses because of their great sensitivity to air oxidation. For instance, Fe(DPM).sub.2 is reported to "char immediately on exposure to air", Fackler et al., Inorg. Chem., 6, 921 (1965); Mn(DPM).sub.2 "charred immediately on contact with air", Hammond et al., Inorg. Chem., 2, 75 (1963); and there is extreme sensitivity of Co(DPM).sub.2 to oxidation, Hammond, supra, page 76, and Gerlach et al., Inorg. Chem., 8, pp. 2293 and 2294 (1969).